Effect of age of worker honey bees (Apis mellifera) on tracheal mite (Acarapis woodi) infestation

The susceptibility of worker honey bees,Apis mellifera L., as a function of age, to infestation by tracheal mites,Acarapis woodi Rennie, was investigated. Bees <24 h old were infested most frequently, and the frequency of infestation declined precipitously thereafter. Bees >4 days old were rarely infested in colonies during active brood rearing. Only 2 of 255 bees >8 days old, and 1 of 246 bees >16 days old, became infested. Most of the eggs found in bees>3 weeks old apparently were produced by the progeny of the original infestation.     

Host preference of the honey bee tracheal mite (Acarapis woodi (Rennie))

Field and laboratory bioassays were used to test the preference of the honey bee tracheal mite,Acarapis woodi (Rennie), for drones versus workers. Groups of newly-emerged drones and workers were marked and introduced into either heavily infested colonies (field bioassays) or into the cages of infested bees obtained from the field colonies (laboratory bioassays). Seven days later all of the marked bees in each bioassay were removed. The numbers of mites of each life stage in each drone or worker target bee of each experiment were quantified. Mite prevalence values for the two castes were not found to differ significantly for either experiment. However, the caste of the target bee was shown to influence the migration of the adult female mites. Drones contained a greater number of migratory female mites and greater total numbers of all mite stages as compared to workers. These results indicate that migrating female mites preferentially infest drones and suggest that the role of drones in the dissemination and population dynamics of the tracheal mite needs to be examined further.     

Influence of resistant honey bee hosts on the life history of the parasite Acarapis woodi

Non-infested, young adult honey bees (Apis mellifera L.) of two stocks were exposed to tracheal mites (Acarapis woodi (Rennie)) in infested colonies to determine how divergent levels of susceptibility in host bees differentially affect components of the mite life history. Test bees were retrieved after exposure and dissected to determine whether resistance is founded on the reduced success of gravid female (foundress) mites to enter the host tracheae, on the suppressed reproduction by foundress mites once established in host tracheae or on both. Cohorts of 30–60 bees from each of ten resistant colonies and eight susceptible colonies were tested in eight trials (three to five colonies per stock per trial) having exposure durations of 4, 9 or 21 days. The principal results were that lower percentages of resistant bees than of susceptible bees routinely became infested by foundress mites, individual infested susceptible bees often had more foundress mites than individual infested resistant bees did and mite fecundity was similar in both host types. The infestation percentage results corresponded well with similar results from a prior field test of these stocks and, thus, suggest that the bioassay is useful for assessing honey bee resistance to A. woodi.     

Phenotypic variation in susceptibility of honey bees,Apis mellifera,to infestation by tracheal mites,Acarapis woodi

A laboratory bioassay was used to study phenotypic differences in susceptibility of honey bees,Apis mellifera L., to tracheal mites,Acarapis woodi Rennie. Significantly different infestation frequencies were found in bees from 23 colonies containing queens that were instrumentally inseminated with single drones. Queens and drones originated from a closed population composed of commercial stock from various areas of the United States.Mites were randomly distributed with respect to right and left prothoracic tracheae. Tracheae containing mites were no more or less attractive to migrating mites than non-infested tracheae. The same quantity of progeny per female was produced in tracheae containing 1–3 mites. Female mites apparently do not migrate a second time after egg laying begins.The degree of phenotypic variation suggests that selection of honey bees for tracheal mite resistance is feasible.     

Evaluation of sampling methods for determining infestation rates of the tracheal mite (Acarapis woodi R.) in colonies of the honey bee (Apis mellifera): Spatial,temporal, and spatio-temporal effects

Current sampling methods for estimating infestation rates of tracheal mites in colonies of the honey bee,Apis mellifera, assume that infested bees are randomly distributed and that temporal fluctuations in infestation rates occur homogeneously throughout the colony. We examined these assumptions. Samples of bees were collected from up to five locations in each of eight colonies, and colonies were sampled several times throughout the year. Estimates of infestation rates varied, depending on the location in the colony from which a sample was obtained. Temporal fluctuations in infestation rates did not always occur homogeneously with respect to sampling location. These results demonstrate that assumptions of current sampling protocols for estimating tracheal-mite infestation rates are often violated. Consequently, estimates derived using these methods may not be accurate, and conclusions based on such estimates may not be valid.     

Genotypic variation in susceptibility of honey bees (Apis mellifera) to infestation by tracheal mites (Acarapis woodi)

Two-way selection for lines of honey bees (Apis mellifera L.) susceptible and resistant to infestation by tracheal mites (Acarapis woodi Rennie) was conducted for two generations. Individuals of the susceptible line were 1.4 and 2.4 times more likely to become infested by female mites after the first and second generations, respectively. These results demonstrate that genotypic variability exsts within North American populations and that selection for resistance is feasible. The mechanisms of resistance are unknown.     

PCR-based detection of a tracheal mite of the honey bee Acarapis woodi

The effects of the tracheal mite Acarapis woodi on the health of honey bees have been neglected since the prevalence of Varroa mites to Apis mellifera colonies. However, tracheal mite infestation of honey bee colonies still occurs worldwide and could impose negative impact on apiculture. The detection of A. woodi requires the dissection of honey bees followed by microscopic observation of the tracheal sacs. We thus developed PCR methods to detect A. woodi. These methods facilitate rapid and sensitive detection of A. woodi in many honey bee samples for epidemiologic surveys.     

New method for rapidly estimating population densities of the concealed wood‐borer Monochamus alternatus (Coleoptera: Cerambycidae) in the field

To rapidly estimate pine sawyer, Monochamus alternatus Hope, population densities in forests, the vertical distributions of M. alternatus oviposition sites and larvae on infested Masson pines (Pinus massoniana Lamb.) were studied. Results showed that the number of oviposition sites on sections of trunks between 0 and 2 m above ground was significantly greater than on sections of trunk above 2 m, and the vertical distribution had a significant logarithmic relationship with trunk height. The larval number of M. alternatus on dead infested trees had a significant difference among heights of trunks. Sections on trunks at 2–4 m usually contained the largest number of M. alternatus larvae, while the number of larvae on trunks above 10 m declined significantly, as well as in the 1 m section of trunk at the base. The vertical distribution of M. alternatus larvae on dead infested pines showed a distinct parabolic relationship with trunk height. The number of oviposition sites of M. alternatus on infested Masson pine trunks revealed a significant exponential relationship with the diameter at breast height (DBH) of trees. A significant positive linear relationship also was observed between M. alternatus larval number and DBH on the host pine trees, as well as between the numbers of larvae and oviposition sites on an individual tree. The total number of larvae in an infested tree could be calculated easily using an established equation, through counting the number of oviposition sites at 3–4 m of trunk aboveground. This study developed a practical method for rapid estimation of M. alternatus populations.     

Single and dual parasitic mite infestations on the honey bee, Apis mellifera L.

Summary: The onset of foraging, proportion of pollen collectors, and weight of pollen loads were compared in individual honey bees (Apis mellifera) infested by zero, one (Acarapis woodi, the honey bee tracheal mite, or Varroa jacobsoni,varroa), or both species of parasitic mites. Phoretic varroa host choice also was compared between bees with and without tracheal mites, and tracheal mite infestation of hosts was compared between bees parasitized or not by varroa during development. The proportion of pollen collectors was not significantly different between treatments, but bees parasitized by both mites had significantly smaller pollen loads than uninfested bees. Mean onset of foraging was earliest for bees parasitized by varroa during development, 15.9 days. Bees with tracheal mites began foraging latest, at 20.5 days, and foraging ages were intermediate in bees with no mites and both, 17.6 and 18.0 days respectively. Phoretic varroa were found equally on bees with and without tracheal mite infestations, but bees parasitized by varroa during development were almost twice as likely to have tracheal mite infestations as bees with no varroa parasitism, 63.9 % and 35.5 %, respectively. These results indicate that these two parasites can have a biological interaction at the level of individual bees that is detrimental to their host colonies.     

Caste, Sex and Strain of Honey Bees (Apis mellifera) Affect Infestation with Tracheal Mites (Acarapis woodi)*

Worker honey bees from genetic strains selected for being resistant (R) or susceptible (S) to tracheal mites typically show large differences in infestation in field colonies and in bioassays that involve controlled exposure to infested bees. We used bioassays exposing newly emerged individuals to infested workers to compare the propensity for tracheal mites to infest queens, drones and workers from R and S colonies. In tests with queens, newly emerged R and S queens were either simultaneously confined in infested colonies (n = 95 and 87 respectively), or individually caged with groups of 5–20 infested workers (n = 119 and 115 respectively). Mite prevalence (percentage of individuals infested) and abundance (foundress mites per individual) after 4–6 days did not differ between R and S queens. In another test, five newly emerged drones and workers from both an R and an S colony, and a queen of one of the two strains, were caged in each of 38 cages with 20 g of workers infested at 60–96% prevalence. Infestations of the R queens (n = 17) and S queens (n = 19) did not differ significantly, but R workers had half the mite abundance of S workers, while R drones received about a third more migrating mites than S drones. In tests to evaluate possible mechanisms, removal of one mesothoracic leg from R and S workers resulted in 2- to 10-fold increase in mite abundance on the treated side, but excising legs did not affect infestation of the corresponding tracheae in drones. This suggests that differences in infestation between R and S workers, but not drones, are largely determined by their ability to remove mites through autogrooming. If autogrooming is the primary mechanism of colony resistance to tracheal mites, selection for resistance to tracheal mites using infestation of hemizygous drones may be inefficient. *The U.S. Government’s right ot retain a non-exclusive, royalty-free licence in and to any copyright is acknowledged.     

The removal response ofApis mellifera L. colonies to brood in wax and plastic cells after artificial and natural infestation withVarroa jacobsoni Oud. and to freeze-killed brood

LikeApis cerana colonies,A. mellifera colonies also show removal response toVarroa-infested brood cells. Infested worker brood cells of artificially and naturally infested combs were detected by the worker bees to various degrees in all types of comb-material used.The bees uncap brood cells and remove larvae or pupae infested with one or two mites. The removal response of worker bees was stronger towards brood cells containing two mites than cells with one mite.The specific signals which cause the removal of brood cells infested withVarroa mites are unknown. Removal response toVarroa-infested brood cells in plastic comb-material (Jenter-and ANP-comb) was significantly higher than to brood in wax combs. Up to now we do not know to what extent this tolerance mechanism is influenced by genetic and environmental factors.Our experiments comparing the removal of freeze-killed brood with the removal of brood infested withVarroa mites demonstrate positive correlations. Considering the time-consuming method of the artificial infestation with living mites, the hygienic behaviour-including the removal of brood cells infested with mites-of large series of colonies can be tested using freeze-killed brood.     

The prevalence of pathogens in honey bee (Apis mellifera) colonies infested with the parasitic mite Varroa jacobsoni

The prevalence of nine honey bee viruses in samples of dead adult bees from Apis mellifera colonies in the Netherlands and Germany infested with the parasitic mite Varroa jacobsoni was compared with virus incidence in uninfested colonies in Britain. In colonies with low mite populations the viruses present and their incidence during the year were similar to the results obtained from British colonies. However, in marked contrast with findings in Britain, acute paralysis virus (APV) was the primary cause of adult bee mortality in German honey bee colonies severely infested with V. jacobsoni. Dead brood from unsealed and sealed infested cells from German colonies with high mite populations also contained much APV. The evidence suggests that V. jacobsoni activates APV replication in adult bees by its feeding behaviour and transmits virus from adult honey bees to pupae. In addition, adult bees, in which APV is multiplying, transmit the virus to unsealed brood in the larval food.     

Host-seeking behaviour of tracheal mites (Acari: Tarsonemidae) on honey bees (Hymenoptera: Apidae)

The behaviour of the endoparasitic tracheal mite, Acarapis woodi (Rennie) on honey bees (Apis mellifera L.) is a challenge to observe because of its small size. Through a microscope, we videotaped this mite's movement on young bees, dead bees and bees exposed to vegetable oil. Previous studies have shown that solid vegetable oil decreases mite infestations in a bee colony. We hypothesized that the oil alters mite behaviour to the detriment of the parasite, thus helping to safeguard the host. Habitat-seeking behaviour, identified as necessary for mites to locate a new host environment, was disrupted on both dead and oil-treated bees. Questing behaviour, which is associated with transfer between hosts, increased significantly on the dead and oily bees. The behaviours of mites were significantly different between all three treatments (x ²=494.96, p<0.001 on dead bees and x ²=851.11, p<0.001 on oily bees). Both questing and seeking behaviours were significantly different on each of the thoracic treatments (F _2,66=7.88, p<0.001 and F _2,66=21.28, p<0.001) and mite questing behaviour was not altered between males and females on live or oily bees (F _1,22=0.25, p<0.62), but habitat seeking was (F _1,22=7.42, p<0.012). The male questing and habitat-seeking behaviours were observed. We conclude that oil-treated bees gained protection from habitat-seeking mites because the normal behaviour of the mites seeking an oviposition site is interrupted.     

A sequential sampling scheme for detecting infestation levels of tracheal mites (Heterostigmata: Tarsonemidae) in honey bee (Hymenoptera: Apidae) colonies

The introduction of parasitic honey bee mites, the tracheal mite, Acarapis woodi (Rennie) in 1984 and the Varroa mite, Varroa jacobsoni, in 1987, has dramatically increased the winter mortality of honey bee, Apis mellifera L., colonies in many areas of the United States. Some beekeepers have minimized their losses by routinely treating their colonies with menthol, currently the only Environmental Protection Agency-approved and available chemical for tracheal mite control. Menthol is also expensive and can interfere with honey harvesting. Because of inadequate sampling techniques and a lack of information concerning treatment, this routine treatment strategy has increased the possibility that tracheal mites will develop resistance to menthol. It is important to establish economic thresholds and treat colonies with menthol only when treatment is warranted rather than treating all colonies regardless of infestation level. The use of sequential sampling may reduce the amount of time and effort expended in examining individual colonies and determining if treatment is necessary. Sequential sampling also allows statistically based estimates of the percentage of bees in standard Langstroth hives infested with mites while controlling for the possibility of incorrectly assessing the amount of infestation. On the average, sequential sampling plans require fewer observations (bees) to reach a decision for specified probabilities of type I and type II errors than are required for fixed sampling plans, especially when the proportion of infested bees is either very low or very high. We developed a sequential sampling decision plan to allow the user to choose specific economic injury levels and the probability of making type I and type II errors which can result inconsiderable savings in time, labor and expense.     

The natural control of the tracheal mite of honey bees

The natural control of the tracheal mite, Acarapiswoodi, of the honey bee depends greatly on good foragingopportunities for bee colonies and on limited competition between colonies. Thesevere, widely-publicised disease of bees, referred to as the Isle ofWight disease in Britain early in the last century when colonies weremore numerous than subsequently, was wrongly attributed to the mite, whichcauses no overt symptoms. The disease was almost certainly caused by beeparalysis virus, which does cause the symptoms and is independent of the mite,and which is similarly associated with large densities of bee colonies.     

The effect of the ectoparasitic mite, Varroa destructor on adult worker honeybee (Apis mellifera) emergence weights, water, protein, carbohydrate, and lipid levels

Wet weight, dry weight and water contents of emerging honeybees (Apis mellifera L. [Hymenoptera: Apidae]) infested with the ectoparasitic mite Varroa destructor (Anderson) (Acari: Varroidae) were all negatively correlated with increasing numbers of mites. It was estimated that for every female mite present during the bees' development, the host would lose three percent of its body water. Parasitised bees also emerged with lower head and abdomen concentrations of protein and with lower abdominal carbohydrate concentrations. Lipid concentrations were not detectably affected by V. destructor infestation. The losses of metabolic reserves were not, however, judged to be serious enough to be directly responsible for the high bee mortality and ultimate colony collapse that are associated with the arrival of Varroa in a hive. Some 8.5% of the emerging bees exhibited morphological deformities and deformity was positively correlated with increasing numbers of mites in brood cells. Deformed bees were, however, found in all categories of parasitosis, suggesting that other factors, such as infectious agents, may be involved. Mites that fed on either live or dead U¹⁴C- labelled bees acquired the label within 24 h and it was calculated that an adult female mite consumes 0.67 l haemolymph 24 h^–1. It was also demonstrated that ¹⁴C was transmitted to a previously non-radio-labelled bee when a mite that had been feeding on a labelled bee changed hosts. The level of transfer was above that which could have arisen through contamination of the mites' mouthparts and supports the suggestion that Varroa is an important vector of pathogens such as viruses.     

The Role of Cuticular Compounds in the Resistance of Honey Bees (Apis Mellifera) to Tracheal Mites (Acarapis Woodi)

This study examined the migration of tracheal mites (Acarapis woodi) into honey bees (Apis mellifera) from different colonies and the relative attraction of mites to hexane extracts from the external body surfaces of young bees. Relative resistance of bees from different colonies initially was assessed with a field bioassay that involved tagging newly emerged bees, pooling them in heavily mite-infested colonies, retrieving them 7 days later, and examining them for tracheal mite prevalence and abundance. For those colonies identified as most resistant and least resistant, cuticular chemicals were extracted in hexane from frozen, newly emerged worker bees. These extracts were presented to individual tracheal mites in pairwise fashion in a laboratory bioassay. The results demonstrated that mites prefer extracts of bees from some colonies more than others, however, no consistent differences were demonstrated. Our inability to predict mite responses to extracts based on our initial assessment of relative resistance indicates that other mechanisms of resistance influence mite success in colonizing new host bees.     

The influence of web monitoring tactics on the tracheal systems of spiders in the family Uloboridae (Arachnida,Araneida)

Summary Uloborids that spin reduced webs more actively monitor them than those that construct orb webs. Hyptiotes use both their first and fourth legs to tense their triangle-webs, whereas Miagrammopes rely principally on their first legs to monitor and jerk the threads of their irregular webs. The respiratory systems of these spiders include tracheae that extend into the prosoma, bifurcate, and enter the legs. To determine if the legs responsible for active web-monitoring tactics have more extensive tracheal supplies, the total cross sectional area has been computed of the tracheae entering the legs of mature female orb web and reduced web uloborids. Each leg's value has been divided by the cross sectional area of the tracheal trunks that enter the prosoma. These indexes reveal no significant differences between the relative tracheal supplies of the orb weavers investigated (Waitkera waitkerensis, Tangaroa beattyi, Uloborus glomosus). But the first, third, and fourth legs of H. cavatus and the first legs of M. animotus and M. pinopus have greater relative tracheal supplies than those of the three orb weaving species. Relative to leg volume, the first and fourth legs of H. cavatus have the greatest and the first legs of Miagrammopes species the next greatest tracheal supplies. When tracheal lengths are considered, these differences in potential oxygen supplies remain, showing that area differences do not simply compensate for differences in the distances over which oxygen must diffuse. These differences are leg-specific and not species-specific, and uloborids with the most extensive tracheal supplies are found in moist habitats. Thus the observed differences are best explained as adaptations to meet the greater oxygen demands of legs responsible for active web-monitoring tactics and not as adaptations to reduce respiratory water loss.     

Essential roles for the Dhr78 orphan nuclear receptor during molting of the Drosophila tracheal system

The Drosophila Dhr78 orphan nuclear receptor has been proposed to play a role in molting of the tracheal cuticle and regulate gene expression during the third larval instar, possibly in response to a novel systemic hormonal signal. Here, we show that there are no essential maternal functions for Dhr78 during development, and that mutants missing both maternal and zygotic Dhr78 function die primarily during second and third instar larval development. We show that defects in the tracheal system can be observed as early as the first instar, manifested as regions of fluid in the dorsal tracheal trunks. In addition, Dhr78 mutant tracheae show a highly penetrant defect in gas filling at the first-to-second instar larval molt. Dhr78 expression in only the tracheal system is sufficient to rescue the lethality of Dhr78 mutants, and selective inactivation of Dhr78 function in the tracheae by targeted RNAi is sufficient to result in tracheal defects. Finally, we see no evidence for widespread activation of the Dhr78 ligand binding domain in third instar larvae using the GAL4-LBD system, arguing against a systemic hormone for the receptor at this stage in development. Taken together, our results indicate that Dhr78 exerts its essential functions during molting of the tracheal cuticle in Drosophila.     

Inheritance of resistance to Acarapis woodi (Acari: Tarsonemidae) in first-generation crosses of honey bees (Hymenoptera: Apidae)

The tendency of honey bees, Apis mellifera L, to become infested with tracheal mites, Acarapis woodi (Rennie), was measured in six different types of F1 colonies. The colonies were produced by mating a stock (Buckfast) known to resist mite infestation to each of five commercially available stocks and to a stock known to be susceptible to mites. Young uninfested bees from progeny and parent colonies were simultaneously exposed to mites in infested colonies, then retrieved and dissected to determine resultant mite infestations. Reduced infestations similar to but numerically greater than those of the resistant parent bees occurred in each of the six crosses made with resistant bees regardless of the relative susceptibility of the other parental stock. Reciprocal crosses between resistant and susceptible queens and drones proved equally effective in improving resistance. Therefore, allowing resistant stock queens to mate naturally with unselected drones, or nonresistant queens to mate with drones produced by pure or outcrossed resistant queens, can be used for improving resistance of production queens.